Heart and lung failure are the most common causes of death in critically ill children in Pediatric Intensive Care Units (PICUs). Hyperglycemia is common, and the timing, intensity, duration and variability of serum glucose are associated with morbidity and mortality. Tight glycemic control (TGC) to normalize blood glucose concentrations with intravenous insulin significantly reduced mortality and morbidity in selected critically ill adult surgical patients, but recent large adult studies show statistically significant increases in mortality and hypoglycemia when TGC is deployed without adequately explicit algorithms or continuous glucose monitoring. The only single-center PICU trial of TGC showed a 55% decrease in 30-day mortality and 10% reduction in PICU length of stay (LOS), despite an extremely high rate of severe hypoglycemia. Theoretical consequences of hypoglycemia in the developing pediatric brain are greater threats than for adults. Therefore, recommendations for clinical practice cannot legitimately be made without a protocol that mitigates these risks. The critical gap in knowledge is whether safe and effective TGC can reduce morbidity and mortality in children with heart and lung failure sufficiently to justify a low risk of hypoglycemia. To evaluate the efficacy of our innovative and safe TGC protocol to reduce mortality and PICU LOS in critically ill children, we will conduct a randomized clinical trial (RCT) in 20 PICUs, called HALF-PINT: Heart and Lung Failure - Pediatric INsulin Titration trial. Patients with cardiovascular and/or respiratory failure who develop hyperglycemia will be randomized to either a Normal-TGC group in which insulin will be infused to reduce glucose concentrations into the normal target range of 80-110 mg/dL or to a High-TGC group in which glucose will be reduced into the higher 150-180 mg/dL range, a range advocated by some adult data. Both groups will receive identical standardized intravenous glucose at an age-appropriate rate in order to provide basal calories and prevent hypoglycemia. Insulin infusions will be titrated with an explicit algorithm combined with continuous glucose monitoring using a system that has been safely implemented in >500 critically ill infants and children. This study will test the primary hypothesis that patients assigned to the NL-TGC group will have a combined outcome of lower mortality and shorter PICU LOS compared with HI-TGC. The protocol will also evaluate the ability of NL-TGC to reduce the rate of accumulation of organ dysfunction, increase ventilator-free days, reduce incidence of nosocomial infections and improve neurodevelopmental outcomes at 1 year after their PICU course. This RCT will have a significant impact on public health in that its results will inform the broad practice of pediatric critical care nationally by providing evidence-based guidance regarding this critically important and controversial issue.